This application claims priority to Korean Patent Application No. 2001-36589 filed on Jun. 26, 2001.
1. Technical Field
The present invention relates to a semiconductor memory device, and more particularly, to a digitally controlled adaptive driver and method thereof for automatically sensing an unknown load coupled to an output terminal of the driver and digitally controlling the current driving ability of the driver.
2. Description of Related Art
In general, a driver is a component of a semiconductor device that drives applications coupled to an output terminal of the driver at a predetermined data output speed. Such applications generally have a capacitive load. The slew rate of a signal output from the driver is dependent on the value of the capacitive load and an amount of current applied to the capacitive load.
FIG. 1 is a black diagram of an adaptive output driver as disclosed in Korean Patent application No. 98-36292. Referring to FIG. 1, the adaptive output driver comprises a load sensing circuit 210 and a buffer circuit 230. The load sensing circuit 210 senses the load of an output terminal OUT (that is coupled to an external bus line) in response to first and second control signals (UP and DN).
The buffer circuit 230 changes an amount of current flowing to the adaptive output driver in response to the outputs (COUT1 and COUT2) of the load sensing circuit 210, thereby changing the driving ability of the adaptive output driver. Therefore, the adaptive output driver is required to have extra pull-down drivers 21-24 to sense the load coupled to the output terminal OUT of the driver and to control the current flowing to the output terminal OUT.
Further, since the adaptive output driver operates based on an analog method, it is difficult to measure the exact value of the capacitive load coupled to the output terminal. Thus, it is difficult to precisely control the amount of current supplied to the capacitive load. Moreover, it is difficult to design an adaptive output driver operated based on an analog method.
It is an object of the present invention to provide a digitally controlled adaptive driver that operates based on a digital method and precisely measures the variable value of the capacitive load coupled to an output terminal of the adaptive driver.
It is another object of the present invention to provide a method for driving a driver that precisely measures the variable value of the capacitive load coupled to an output terminal of the driver.
According to one aspect of the present invention, there is provided a digitally controlled adaptive driver comprising a load sensing circuit for sensing a voltage of an output terminal of the driver connected to a load and for generating a control signal in response to the voltage of the output terminal, and a control driver for digitally determining a value of the load coupled to the output terminal in response to the control signal of the load sensing circuit and for controlling a driving current for driving an input signal in response to the value of the load.
In one embodiment, the driver further comprises a charge pumping circuit for supplying a reference current to the output terminal in response to a clock signal.
The load sensing circuit preferably comprises a reference voltage generator for generating a reference voltage, and a comparator for comparing the reference voltage of the reference voltage generator with the voltage of the output terminal and for outputting the comparison result as the control signal. The control signal comprises a first state when the voltage of the output terminal is larger than the reference voltage, and the control signal comprises a second state when the reference voltage is larger than the voltage of the output terminal.
The control driver comprises a counter for counting the number of cycles of a clock signal and for outputting a digital signal corresponding to the number of cycles of the clock signal in response to the control signal having the first state, a digital-to-analog converter (DAC) for converting the digital signal into the driving current, and a driver for driving the input signal into the output terminal in response to the driving current.
According to another aspect of the present invention, it is provided a digitally controlled adaptive driver comprising a charge pumping circuit for supplying a predetermined current to an output terminal of the driver in response to a clock signal, a counter for counting the number of cycles of the clock signal and for outputting a count signal corresponding to the number of counted cycles of the clock signal, a driver for driving an input signal to the output terminal in response to the count signal, and a control signal generator for comparing the voltage of the output terminal with a reference voltage to generate a control signal. The control signal has a first state when the voltage of the output terminal is larger than the reference voltage, and the control signal has the second state when the reference voltage is larger than the voltage of the output terminal. The charge pumping circuit is enabled in response to the second state of the control signal, and the counter outputs the count signal in response to the first state of the control signal.
According to further aspect of the present invention, it is provided a method for driving a signal. The method comprises the steps of sensing a voltage of an output terminal connected to a load, generating a control signal based on the sensed voltage, digitally measuring the load in response to the control signal, and adaptively controlling a driving current in response to the value of the load to drive an input signal to the output terminal.